Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The photoresist coated on the substrate is next subjected to an image-wise exposure to radiation.
The radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation exposed or the unexposed areas of the photoresist.
The trend towards the miniaturization of semiconductor devices has led to the use of new photoresists that are sensitive to lower and lower wavelengths of radiation and has also led to the use of sophisticated multilevel systems to overcome difficulties associated with such miniaturization.
There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a deprotection reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying surface is uncovered.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature, which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less than one micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate. This becomes even more critical as the push toward miniaturization reduces the critical dimensions on the devices.
It is desirable and advantageous to have photoresist compositions that result excellent photospeed properties, depth of focus and sidewall profile geometries. Especially for thick film resists (e.g., >20 micrometers (μm)), fast photospeeds are desirable. The present invention provides such photoresist compositions.
U.S. Pat. Nos. 4,294,909 and 4,356,252, inventor Lee, issued Oct. 13, 1981, and Oct. 26, 1982 respectively, discloses a photosensitive element which comprises a support bearing a layer of negative-working tonable photoimaging composition comprising at least one organic polymeric binder (a), a photosensitizer (b) which generates an acid upon absorption of actinic radiation, and at least one compound taken from the group of as defined in the patents, binder (a) being plasticized by the decomposition product of either compound (c) or (d) or the combination thereof. The photosensitive element is useful in making color proofs.
Japanese patent application JP9031044, inventor Atsushi, Sumitomo Chemical Co., discloses that to solve the problem of producing an azide-based photosensitizer capable of shortening the filtration time with a crystal having a large grain diameter at a high reactional rate by using 1,3-dioxolane without any problem in safety as a reactional solvent, a compound having phenolic hydroxyl group (e.g. 2,3,4,4′-tetrahydroxybenzophenone) is condensed with a 2-naphthoquinone diazide-4- or a 2-naphthoquinone diazide-5-sulfonyl halide (e.g. 1,2-naphthoquinone diazide-4- or 2-naphthoquinone diazide-5-sulfonyl chloride) in a solvent containing 1,3-dioxolane to afford a naphthoquinone diazide-based photosensitizer. The reaction is preferably carried out in the presence of a base and triethylamine, etc., are used as the base. The base is preferably used at 1.05-1.3 molar ratio to the 1,2-naphthoquinone diazide-4 or 1,2-naphthoquinone diazide-5-sulfonyl halide.